Fuel in the Airbox

[calmck49]

Why do I keep ending up with fuel in my airbox. I have 2 xs11 one made 11/78 and the other 6/79 and they both keep getting fuel in the airbox. Do the carbs need rebuilt or can someone tell me which part specifically is causing this.

[prometheus578]

"I can't stop passing gas!"

Two issues at play here.
Petcocks not turning off: When there's no engine vacuum, the petcocks shouldn't allow fuel to flow.

Oft' times, there's a lot of rust and crud from the fuel tank that get's lodged against the petcock diaphram O ring, stopping it from seating fully.
Pull the tank, pull the petcocks, open 'em up and check.
Next issue...
Even if the petcocks do leak, the float needles should stop the flow of fuel into the carb. They obviously aren't.
As the fuel in the bowl rises, the floats push upward on the float needles, stopping the flow.
Age and grit wear a ring on the needle's tapered sealing area, hence the leak.
Float needles must be replaced. Use a Q tip and some chrome polish and clean up the seat where the needles seal, too.
HHMMmm.. an afterthought...
You didn't supply enough info....
If the airbox floods when the bike is running, check the floats and float needles.
If it floods when sitting, check both the petcocks and needles.

[wa407mpp]

petcocks.

My bet is on the petcocks needing rebuild kits. My bike did that a couple of years ago and rebuilding the petcocks fixed it. If the tank is full and the petcocks are weak the gas in the tank will overpower the petcocks and over fill the flout bowel until the fuel seeps back out the carb throats and into the air box. I don't know how it gets past the float valves, but it does, maybe through another passage. By the way raw gas will ruin a good K&N air filter , it hardens the rubber so once you take it off for cleaning it won't go back on. My bike would run rich and foul the plugs for no reason ,and with no outward signs of a leak anywhere,but with a strong gas smell. When I pulled the filter cover it was half full of gas. Well anyway that's my story on the subject and I'm sticking to it.

[calmck49]

Fuel in airbox

When I remove the airbox and run with out box no fuel comes from the back of the carbs. Not even a drop. I do have an occasional back fire in #2. When I removed box the back of 3 and 4 carbs were wet so I thought I would see the fuel coming from there. With airbox off it seems to run great. Do I just put some K&N filters on and keep marching. I don't understand why it would do it only when air box is on.

[79XS11F]

Also make sure the carb vent hoses and tubes they connect to in the air box are not plugged.
Rob

[planedick]

Vent hoses

Vent hoses is the most probable path from overfilled carb bowls to the airbox. Just putting on pod filters is a very tempory fix and is bound to leave you with more trouble than you want. Best is to check the floats, needles and petcocks. Improper maintenance will make it a parts bike in a hurry.

[prometheus578]

Planedick, you may have just typed a little too quickly.
Fuel does not get into the airbox through the vent hoses. The vent outlet on the carb is above the level of the bowl, and then the hose usually routes upward.
Fuel gets into the airbox by first coming out from the airjets in the carb horn, as they are the lowest opening on that side, and then, depending on how quickly the bowl fills, up through the mainjet/needle jet.
The deal with the vent hoses.... if the carbs can't vent, then when fuel tries to fill the bowl the air can't escape to make room. Causes an overpressure, changes the bouyancy of the floats, they then don't float upward... so the needle can shut off the flow, etc.
Might want to check to see if there's a lot of fuel in your oil, as well. Carbs overflow in both directions, you know.

[egsols]

Had same problem this summer. Go out for a ride, come back, shut off bike and a little later found fuel in airbox. Ran without airbox, no fuel leaking. Took airbox apart, cleaned, re-assembled, blew out both vent hoses as well as tees to carbs. End result...no more fuel in airbox. Definitely vent hoses in my case, however, make sure their not clogged at the tees also.

[calmck49]

fuel in airbox

It only fills up when it is running and then drains when it is off. I don't think it is the pet cock or else it would be reveresed right??? Still can't figure out why it only does it when it is off. I will adjust the float on 3 and 4 today and see how that does. It is definitely coming from the rear horn on 4 possibly 3 but when the bike is on the side stand it may have just been leaking into 3 and making it look bad. How come those K&N filters are a bad idea. I thought that was a pretty good brand of filter? Is it just because that is not the way it is designed?

[TucmanXJ]

Fuel going THRU airbox

My little time bandit adventure rebuilding 4 carbs last week was prompted by purchasing a 1979 F model then discovering to my horror that FUEL was DRAINING STRAIGHT thru the Airbox onto the pavement below.

NEXT: Drained the oil as the crankcase was CHOCK FULL of volatile fuel & oil mix. This nasty stuff will KILL your bike's engine quick!

Tore apart the 4 carbs. WHAT did I find? TWO Mikunis had developed leaking bowl inlet valves e.g. the brass seats & tiny float needles were full of fuel trash / gunk. It was a real mess.

Cleaned 'em, and replaced all lower carb parts: seats, needles, jets to be on the safe side. VOILA! NO MORE FUEL LEAKING-OVERFLOWING-THRU-AIRBOX scene. Whew!

My recommendation, Do all the Above: Rebuild the carbs & the Petcocks. BY-the-WAY; dirty / gummy petcocks will cause the bike NOT to run at all (unless set on PRIME)!

I'm placing a bet / keeping my fingers crossed that the PO did NOT run the bike like a TWO-STROKE for long ... otherwise it's gonna be rebuild time.

RJ

[egsols]

You say it fills when running but wihtout air box it's dry? How can you tell its filling the box with the box on?

[calmck49]

Because it is leaking out around the seam and when I take off the bottom it has a good quart in it. I think I found the problem. The three and four carbs were totally gunked out. My left side petcock is dirty also. Think it was contaminating the carbs. Let you guys know shortly.

[Incubus]

I've had fuel in my air box so often I have considered using it as a reserve fuel tank.

I hate my petcocks. Hate them.

Patrick

[calmck49]

Get this I got the one bike running perfect. No more fuel in air box. Get suited take it out 100' later shift into second and it is blown. Second gear just crapped the bed. Yeah putting the other set of carbs on the other bike now. What a good day..

[mro]

I hate my petcocks

Standard petcocks are easy to rebuild and parts are about $20.00
Good idea to clean em up inside and polish the surfaces over the rubber goodie with the 4 holes.
==========

100' later
Bummer calmck49

Maybe it's the way I shift?
I have yet to have a gear problem


mro